1. Field of the Invention
The present invention relates to a method for production of ferroelectric thin films and, more particularly, a method for depositing thin films of barium titanate on desired substrates without use of complex procedures.
2. Description of the Prior Art
Barium titanate, BaTiO.sub.3, has been utilized widely for various electronic devices such as, ultrasonic sensors, capacitors, actuators, pyroelectric infrared detectors and nonvolatile memories, because of its superior properties as a ferroelectric, piezoelectric or pyroelectric material. Further, many investigations have been directed to the application of barium titanate to many other fields.
In such devices, barium titanate is generally applied as thin films to make the best use of its properties. For this reason, there have been proposed various methods for production of thin films of barium titanate in various patent documents and literatures such as, JP-A-S61-30678, JP-A- H2-94209, JP-A- H2-258700, and JAPANESE JOURNAL OF APPLIED PHYSICS, Vol. 28, No. 11, 1989.
JP-A- 61-30678 discloses a method including the step of chemically converting a metallic titanium surface serving as a substrate to a barium titanate. However, this method is limited only to metallic titanium as the substrate, thus making it impossible to form thin films of barium titanate on other substrates.
JP-A- H2-94209 discloses a sputtering process in which a material is sputtered from a target and deposited on the substrate. However, sputtering requires use of complex, expensive equipments, resulting in considerable increase of equipment investment.
JP-A- H2-258700 discloses a plasma method utilizing plasma for deposition of thin films. This method requires complex, large-scale equipments and can be applied only to substrates which can withstand high temperatures.
The JAPANESE JOURNAL OF APPLIED PHYSICS discloses a hydrothermal, electrochemical method in which thin films are deposited on a substrate by a wet process at high temperature and high pressure in an autoclave. Since the substrate is used as one of electrodes, this method can be applied only to metal substrates with good conductivity. Further, the formation of thin films is performed at high temperature and pressure, thus making it impossible to apply this process to organic substrates.
On the other hand, it is also known that barium titanate can be produced in a powder form by hydrolyzing titanium alkoxide in a solution containing barium ions at low temperatures. However, it is impossible with the known hydrolyzing process to produce thin film of barium titanate.